Double mitered compensated waveguide bend

ABSTRACT

A double mitered, compensated waveguide bend having a low VSWR over a wide bandwidth in which the effective width of the waveguide in the plane of the bend is narrowed at the mitered corners and increased on a line bisecting the angle of the bend.

United States Patent Albee DOUBLE MITERED COMPENSATED WAVEGUIDE BEND[72] Inventor: Thomas K. Albee, Western Springs,

[73] Assignee: The Bunker-Ramo Corporation,

Oak Brook, 111.

[22] Filed: March 8, 1971 [21] App1.No.: 122,104

Related US. Application Data [63] (llggiginuation of Ser. No. 819,294,April 25,

52 us. or ..333/98 BE, 333/33, 333/34 51 int. Cl. ..1-101p l/02,1-l0lp5/00 58 Field of Search ..333/98 BE, 98 R, 33, 34

[56] References Cited UNITED STATES PATENTS 2,640,877 6/1953 Miller eta1. ..333/98 BE 1 Aug. 22, 1972 2,810,111 10/1957 Cohn ..333/98 BE3,072,870 1/ 1963 Walker ..333/98 BE 3,157,844 11/1964 Lanctot ..333/98S OTHER PUBLICATIONS Marshall et al., Precision Waveguides, TheEngineer, Western Electric, Vol. 1, No. 1, 1- 1957, pp. 35- 41 Ragan, G.L., Microwave Transmission Circuits, McGraw Hill, 1948, pp. 203 217Primary Examiner-Herman Karl Saalbach Assistant Examiner-Wm. H. PunterAttorney-Frederick M. Arbuckle 5 7 ABSTRACT A double mitered,compensated waveguide bend having a low VSWR over a wide bandwidth inwhich the effective width of the waveguide in the plane of the bend isnarrowed at the mitered comers and increased on a line bisecting theangle of the bend.

27 Claims, 6 Drawing Figures atented Aug. 22, 1972 INVENTOR Tl/oms k.1555 DOUBLE MITERED COMPENSATED WAVEGUIDE BEND This application is acontinuation of application Ser. No. 819,294, filed Apr. 25, 1969.

BACKGROUND OF THE INVENTION by swung between the center lines of thestraight waveguide sections is generally three-quarters of a wave lengthof the energy transmitted or more'in odd multiples of quarter wavelengths at the center band frequency. This construction provides a lowVSWR with an inherent broad bandwidth but the size limitation is deemedundesirable for many applications.

Attempts to shorten thelength of the radius of the waveguide bend to thepoint where the two straight waveguide sections are disposed at rightangles to each other have been attempted. While these bends relaxsomewhat the space requirements, they, tend to be frequency sensitiveand difficult to impedance match over the full frequency range. Inattempting to improve the bandwidth, the prior art has increased theradius of curvature of the arc joining the two straight sections ofwaveguide thus narrowing the horizontal dimension of the waveguide inthe area of the bend. Vertical conductive posts or irises disposed atthe junctions of the straight sections of the waveguide to-the radiusbend have been utilized.

An alternative prior art approach has been to utilize double miteredbends in which a section of waveguide disposed intermediate to the tworight angle waveguide sections at an angle of 45 to both. This in effectaccomplishes two abrupt 45 angle changes in the longitudinal directionof the waveguide. This type of construction also provides a low VSWR butonly for a very narrow bandwidth which renders the bend unsuitable formany applications without compensation.

Attempts to compensate for the deficiencies of the double mitered 90bend have included the utilization of conductive posts or irisesdisposed within the waveguide bend substantially on a line where theintermediate section joins each of the two straight sections. Theseposts extend vertically between the top and bottom of the waveguide bendand may alternatively be spaced from the outer vertical walls orcontiguous to the inside vertical wall of the waveguide at the 45 bends.

Inasmuch as mitered waveguide corners exhibit very narrow bandwidths,and cannot be used'without an appropriate matching device forcompensation, the mitered corners are desirably spaced in such a waythat their reflections cancel each other at the bend frequency for whichthe waveguide is designed.

radius bends, the mean or center line length of the arc; 2Q

While this latter type of waveguide bend construction has resulted inimproved performance, the bandwidth at a low VSWR does not approach thatof the present invention. It is accordingly an object of the presentinvention to obviate the deficiencies of the prior art and to provide anovel double mitered waveguide bend small in size relative to the wavelength of the energy propagated therethrough.

- Another object of the present invention is to provide a novel doublemitered waveguide bend having an impedance profile substantiallyidentical for all sections to thereby provide an impedance match overthe entire bandwidth of the energy propagated therethrough.

Still another object of the present invention is to provide a novelright angle waveguide bend having an odd number and not less than threereflections.

Yet another object is to provide a novel double mitered waveguide bendhaving an even number not less than four discrete sections.

These and other objects and advantages of the present invention will bereadily apparent to one skilled in the art to which the inventionpertains from a perusal of the claims and the following detaileddescription of a preferred embodiment of the invention when read inconjunction with the appended drawings.

THE DRAWINGS FIG. 1 is an exploded pictorial view of a preferredembodiment of the double mitered right angle waveguide bend of thepresent invention;

FIG. 2 is a top plan view of the lower portion of the waveguide bend ofFIG. 1;

FIG. 3 is a schematic top plan view of a second embodiment of thewaveguide of the present invention;

FIG. 4 is a schematic top plan view of a thirdembodiment of thewaveguide of the present invention;

FIG. 5 is a schematic top plan view of a fourth embodiment of thewaveguide of the present invention; and

FIG. 6 is a schematic top plan view of a fifth embodiment of thewaveguide of the present invention.

THE DETAILED DESCRIPTION With reference to FIG. 1, a block 10 ofelectrically conductive material may be machined or otherwise groovedfrom the upper surface 12 thereof to the horizontal dimensionshereinafter described. A second planar block 13 of electricallyconductive material may be applied to the upper surface 12 of the lowerblock 10 to provide the fourth wall, i.e., the top wall, of thewaveguide within the bend. I I

It is important that high conductivity materials be utilized in theconstruction of the bend since the two most significant losses are duerespectively to the resistive component of the waveguide material andthe resistive material of the inductive posts or irises hereinafterdescribed.

Assuming that the plane of the waveguide bend is in the X or horizontalplane, the rectangular waveguides have a horizontal or electrical I-Iplane dimension X and a vertical or electrical E plane dimension Y, andare adapted to be connected to the two openings 14 and 16in thewaveguide bend as illustrated in FIG. I.

In accordance with the present invention, the vertical dimensions arethe same throughout the bend in the plane normal to the plane of thebend, i.e. the E plane. The vertical dimensions are moreoversubstantially identical to the vertical or E plane dimensions-of thestraight sections of waveguide to be secured thereto. The horizontaldimension of the waveguide bend in the plane of the bend, i.e. the Hplane, is reduced relative to the horizontal or H plane dimensions ofthe straight sections of waveguide adjacent the corners or junctionthereof with a section disposed generally at an angle of 45 thereto. Thedimension of this generally 45 section in the plane of the bend, thehorizontal or H plane, is increased at the center thereof along a linebisecting the angle of the bend.

With reference now to FIGS. 1 and 2, the vertical wall 17 of the centersection of the waveguide bend may be faired smoothly into the verticalwalls of the two straight waveguide sections (not shown) by machining orotherwise grooving the upper surface 12 of the conductive block to formarcuate surfaces 18 having a radius R. The surfaces 18 may be tangent tothe vertical walls of the straight sections of waveguide at the openings14 and 16 of the bend and tangent as well to the vertical wall 17 of thecenter wall section 17 of the generally 45 section of the bend. The arcsof the surfaces 18 may be swung from a center 19 on a line drawn to thelongitudinal axis of the straight waveguide section at an angle ofone-quarter of the angle of the bend, and having a radius of betweenabout 1 18 to 120 percent of the horizontal dimension X of thewaveguide. The distance between the centers 19 may be between about 58and 60 percent of the horizontal dimension X of the waveguide, raised toa power of The impedance compensating reduction in the horizontaldimension of the waveguide may be accomplished in the illustratedembodiment by machining or otherwise grooving the bend to leave theconductive vertical walls of the block 10 as defined by a first pair ofsurfaces 23 and 27, intersecting, respectively, a second pair ofsurfaces 24 and 26 on the inside of the bend extending transversely intothe waveguide as illustrated at points 28 and 30, substantially alongaline bisecting the angle formed by the junction of the straightwaveguide sections and the center section of the bend disposed generally45 thereto, i.e., the one-quarter of the angle of the bend linereferenced above.

The narrowest horizontal dimension of the waveguide bend as measuredalong both of these onequarter of the angle of the bend lines is betweenabout. 91 and 95 percent of the horizontal dimension X of the waveguide.

The increased horizontal width of the waveguide may be obtained bymachining or otherwise grooving the inside vertical wall of the bendbetween points 28 and 30 of the narrowest dimensions. The maximum widthof the waveguide in the bend may be at a point on the line of symmetryof the bend, i.e., the line normal to the outer vertical wall 17, toabout 104 to 105 percent of the horizontal dimension X of the waveguide.

cel at the center band design frequency. The cancellation of thesemulti-mode reflections requires an odd number, three or more, ofreflection generating means within the bend. An even number, four .ormore, of discrete sections of waveguide are thus present in the bend. i

The impedance Z seen looking along one of the straight sections of therectangular waveguide into the opening 14 is converted to an impedance Zat the apex 28, i.e., the first reduction in the horizontal dimension ofthe waveguide. The impedance Z of the section beginning at the apex 28is converted to an impedance 2;, at the center of the bend, i.e., theenlarged horizontal dimension at point 20. The impedance Z lookingtoward the opening 16 from the center of the bend is reconverted by thereversal in the angle of the internal vertical wall 26 to an impedance ZThe impedance change at the apex reconverts the impedance Z to that ofthe rectangular waveguide, i.e., Z,. An impedance match and cancellationof the multi-mode reflection is thus attained along the line of symmetryof the waveguide bend. The energy propagated through the bend sees anodd number of reflections and an even number of discrete sectionsarranged symmetrically to effect the multi-mode cancellation.

As is well known, the electrically conductive irises at the inside ofthe bend may be replaced by vertical posts disposed alternatively bothat the inside or both at the outside of the bend adjacent the verticalwalls thereof. A good electrical connection should be establishedbetween the inductive posts and the waveguide and the posts should behighly conductive to reduce the losses due to the resistivity of theposts.

Other embodiments of the waveguide of the present invention areillustrated in FIGS. 3-6. With reference, for example to FIG. 3, theouter wall of the bend may be defined by straight sections 50 and 52coplanar with the side walls of the waveguides and by a planar section54 intersecting both of the sections 50 and 52 at an angle one-half ofthe angle of the bend, e.g., for a 90 bend.

The inside wall of the bend may be defined by straight sections 56 and58 coplanar with the walls of the waveguides. An arcuate surface 60 mayconnect the surfaces 56 and 58. The center for the arc of the surface 60must lie substantially on a line normal to and bisecting the section 54of the outer wall, i.e., at the line bisecting the angle of the bend.The center for the arcuate surface 60 may lie on or nearthe surface 54so that the junction of the arcuate surface 60 with each of the surfacesof the straight sections 56 and 58 is substantially on a line passingthrough the junction respectively of the straight sections and 52 withthe section 54 and bisecting the angle formed thereby. This line willhereinafter be known as the one-quarter angle line.

The point of maximum horizontal waveguide width is thus on the line ofsymmetry earlier described to provide the necessary increase in thedimension of the waveguide in the plane of the bend as discussed supra.

The effective narrowing of the horizontal dimension of the waveguide inthe plane of the bend may be accomplished by the use of conductive posts62 disposed on the one-quarter angle lines earlier described. Theseposts 62 may be spaced from the walls of the waveguide but are desirablyplaced as close as possible to reduce the post current.

A third embodiment of the present invention is illustrated in FIG. 4 inwhich the surfaces 50, 52 and 5 4 define the outside wall of the bend asearlier described in connection with FIG. 3. Similarly, the inside wallof the bend may include the straight surfaces 56 and 58.

The widening of the horizontal dimension of the line of symmetry mayhowever be achieved by vertical planar surfaces 64 and 66 joining thesurfaces 56 and 58 respectively on the one quarter angle lines earlierdescribed and mutually intersecting on the line'of-symmetry of the bend,the one half angle line.

The effective narrowing of the horizontal dimension of the waveguide maylikewise be accomplished by means of vertical posts 68 located in thisembodiment adjacent the junction of the inside wall surface 56 with thesurface 64 and the surface 66 with the surface 58.

Still another embodiment of the invention is illustrated in FIG. 5 inwhich the straight surfaces .56 and 58 on the inside of the bend arejoined at the one-quarter angle lines by a planar surface 70. Thestraight surfaces 50 and 52 on the outside of the bend may be joinedrespectively on the one quarter angle lines by surfaces 72 and 74 whichmutually intersect on the line' of symmetry of the bend. An increase inthe horizontal dimension of the waveguide on the line of symmetry isthus achieved. The surfaces 72 and 74 may, of course be replaced by anarcuate surface as shown in FIG. 6 where the radius for the arcuatesurface 51 is between about 107 and 109 percent of the dimension of the.waveguide in the plane of the bend.

The effective narrowing of the dimension of the waveguide in the planeof the bend may be achieved by vertical posts 76 contiguous with thejunction of the surfaces 56 and 70 and the junction of the surfaces 70and 58.

The term substantially normal to the line bisecting the angle of thebend is intended, for example, to encompass the combination of thesurfaces 24 and 26 of FIG. 2, the combination of the surfaces 64 and 66of FIG. 4, the combination of the surfaces 72 and 74 of FIG. 5, thearcuate surface 60 of FIG. 3, and the arcuate surface 51 of FIG. 6.

As will be readily apparent to those skilled in the art, the presentinvention may be embodied in many forms means within said housingadjacent each of said ports, the cross-sectional dimensions of thewaveguide within said housing being substantially uniform in the planenormal to the bend, the sidewall of the bend on the outside of the bendbeing defined by:

a first surface substantially coplanar with one wall of the waveguideexternally of said housing adjacent one of said ports,

a second surface substantially coplanar with one wall of the 'waveguideexternally of said housing adjacent the other of said ports, and I athird surface connecting said first and second surfaces, said thirdsurface being generally arcuate away from the sidewall on the inside ofthe bend so that the cross-sectional dimension of the waveguide withinsaid housing in the plane of the bend along a line bisecting the angleof the waveguide bend is greater than the corresponding dimension of thewaveguide.

2. The waveguide bend of claim 1 wherein the angle of the waveguide bendis 90 and wherein the plane of the waveguide bend is the H plane.

without departing from the scope thereof. By the use of the embodimentof FIG. 1 in an X band waveguide having dimensions of 0.4 by 0.9 inch, aVSWR between 1.010 and 1.090 has been achieved for a band width of 8 to12.6 gigahertz.

This bend has been accomplished in a block 1.5 inches square in theplane of the bend.

The bend of the present invention is also suitable for bends in the Eplane with a caveat as to the amount of power that may be appliedwithout voltage breakdown.

It is intended therefore that the invention not be limited 3. Thewaveguide bend of claim 1 wherein the sidewall of the bend in the insideof the bend is defined by:

a surface substantially coplanar with one wall of the waveguideexternally of said housing adjacent one of said ports, I

a second surface substantially coplanar with one wall of the waveguideexternally of said housing adjacent the other of said ports, and

a third surface connecting said first and second surfaces, said thirdsurface being substantially normal to said line bisecting the angle ofthe bend.

4. The waveguide bend of claim 1 wherein said impedance compensatingmeans are located adjacent the sidewall on the inside wall of the bend.

5. The waveguide bend of claim 1 wherein the dimension of the bend onsaid line bisecting the angle of the bend is between about 104 and 105percent of the dimension of the waveguide in the plane of the bend.

6. The waveguide bend of claim 5 wherein the angle of the waveguide bendis and wherein the plane of the waveguide bend is the H plane; and,

wherein the sidewall of the bend in the inside of the bend is definedby:

a first surface substantially coplanar with one wall of the waveguideexternally of said housing adjacent one of said ports,

a second surface substantially coplanar with one wall of the waveguideexternally of said housing adjacent the other of said ports, and

a third surface connecting said first and second surfaces, said thirdsurface being substantially normal to said line bisecting the angle ofthe bend.

7. A broadband, low VSWR, double mitered waveguide bend for a hollowpipe waveguide having rectangular cross-sectional dimensions comprisinga waveguide bend defining housing having two ports adapted to be alignedwith the waveguide for the efiicient transmission of electromagneticenergy through said housing and having impedance compensating meanswithin said housing adjacent said ports, the cross-sectional dimensionsof the waveguide within said housing being substantially uniform in theplane normal to the bend, the sidewall of the bend on the outside of thebend comprising two discrete surfaces intersecting in a plane bisectingthe angle of the bend, said intersecting surfaces forming an obtuseangle facing the sidewall on the inside of the bend so that thecross-sectional dimension of the waveguide within said housing in theplane of the bend along a line bisecting the angle of the waveguide bendis greater than the corresponding dimension of the waveguide.

8. The broadband of claim 7 wherein the dimension of the bend on saidline bisecting the angle of the bend is between about 104 and 105percent of the dimension of the waveguide in the plane of the bend.

9. The waveguide bend of claim 8 wherein the sidewall of the bend on theinside of the bend is defined by:

a first surface substantially coplanar with one wall of the waveguideexternally of said housing adjacent one of said ports,

a second surface substantially coplanar with one wall of the waveguideexternally of said housing adjacent the other of said ports, and

' a third surface connecting said first and second surfaces, said thirdsurface being substantially normal to said line bisecting the angle ofthe bend; and

wherein said impedance compensating means comprises an element ofelectrically conducting material adjacent the sidewall on the inside ofthe bend.

10. The waveguide bend of claim 9 wherein the angle of the bend is 90and wherein the plane of the bend is the H plane.

11. The broadband of claim 7 wherein the angle of the bend is 90 andwherein the plane of the bend is the H plane.

12. A broadband, low VSWR, double mitered waveguide bend for a hollowpipe waveguide having rectangular cross-sectional dimensions comprisinga waveguide bend defining housing having two ports adapted to be alignedwith the waveguide for the efficient transmission of electromagneticenergy through said housing and having impedance compensating meanswithin said housing adjacent said ports, the cross-sectional dimensionsof the waveguide within said housing being substantially uniform in theplane normal to the bend, the sidewall of the bend on the'inside of thebend comprising two discrete surfaces forming at their intersection on aline bisecting the angle of the bend an obtuse angle facing the sidewallof the bend on the inside of the bend so that the cross-sectionaldimension of the waveguide within saidhousing in the plane of the bendalong said line bisecting the angle of the bend is greater than thecorrespondingdimension of the waveguide.

13. The waveguide bend of claim 12 wherein the sidewall of the bend onthe outside of the bend is defined by:

a first surface substantially coplanar with one wall of the waveguideexternally of said housing adjacent one of said ports,

a second surface substantially coplanar with one wall of the waveguideexternally of said housing adjacent the other of said ports, and,

a third surface connecting said first and second surfaces, said thirdsurface being substantially normal to said line bisecting the angle ofthe bend.

14. The waveguide bend of claim 12 wherein the angle of the waveguidebend is 90, and wherein the plane of the waveguide bend is the H plane.

15; The waveguide bend of claim 12 wherein the waveguide bend as definedby said sidewalls includes an even number of waveguide sections, a firstpair of said sections being of equal length and wider in crosssection inthe plane of the bend at their intersection on said line bisecting theangle of the bend than on their respective intersection with one of asecond pair of said waveguide sections, said second pair of saidsections being of equal length and being wider in cross-section in theplane of the bend at said ports than at their respective intersectionwith said first pair of sections.

16. The waveguide bend of claim 15 wherein the number of waveguidesections in the bend is four and wherein the dimension of the bend inthe plane thereof on a line bisecting the angle of the bend is betweenabout 104 and 105 percent of the dimension of the waveguide in the planeof the bend.

17. The waveguide bend of claim 16 wherein the angle of the bend is 90,and wherein the bend is the H plane.

18. The waveguide bend of claim 12 wherein the sidewall of the bend onsaid outside of said bend is cent of the dimension of the waveguide inthe plane of the bend.

20. A broadband, low VSWR, double rnitered waveguide bend for a hollowpipe waveguide having rectangular cross-sectional dimensions comprisinga waveguide bend defining housing having two ports adapted to be alignedwith the waveguide for the efficient transmission of electromagneticenergy through said. housing, the cross-sectional dimensions of thewaveguide within said housing being substantially uniform in the planenormal to the bend, said waveguide bend including an even number ofwaveguide sections, a first pair of said sections being of equal lengthand wider in cross-section in the plane of the bend at theirintersection on a line bisecting the angle of the bend than on theirrespective intersection with one of a second pair of said waveguidesections,

tions is between about 91 and 95 percent of the dimension of thewaveguide in the plane of the bend.

22. The waveguide bend of claim wherein the dimension of the waveguidebend in the plane of the bend at the intersection of said first pair ofsections is between about 104 and 105 percent of the dimension of thewaveguide in the plane of the bend.

23. The waveguide bend of claim 22 wherein the dimension of thewaveguide bend in the plane thereof at the intersection of said firstand second sections is between about 91 and 95 percent of the dimensionof the waveguide in the plane of the bend.

24. The waveguide bend of claim 23 wherein the plane of the bend is theH plane; and wherein the angle of the bend is 90.

25. The waveguide bend of claim 20 wherein the angle of the waveguidebend is 90 and wherein the plane of the bend is the H plane.

26. The waveguide bend of claim 25 wherein the number of waveguidesections is four, and wherein the dimension of the bend in the plane ofthe bend along said line bisecting the angle of the bend is betweenabout 104 and 105 percent of the dimension of the waveguide in the planeof the bend.

27. A broadband, low VSWR, double mitered waveguide bend for a hollowpipe waveguide having rectangular cross-sectional dimensions comprisinga waveguide bend defining housing having two ports adapted to be alignedwith the waveguide for the effi' cient transmission of electromagneticenergy through said housing, the cross-sectional dimensions of thewaveguide within said housing being substantially uniform in the planenormal to the bend,

the effective cross-sectional dimension of the waveguide within saidhousing in the plane of the bend along a line bisecting the angle of thewaveguide bend being greater than the corresponding dimension of thewaveguide, and,

the effective cross-sectional dimension of the waveguide within saidhousing in the plane of the bend adjacent said ports being less than thecorresponding dimension of the waveguide, said differing effectivecross-sectional dimensions interacting to reduce the VSWR of the bendover a broadband of frequencies.

1. A broadband, low VSWR, double mitered waveguide bend for a hollowpipe waveguide having rectangular cross-sectional dimensions comprisinga waveguide bend defining housing having two ports adapted to be alignedwith the waveguide for the efficient transmission of electromagneticenergy through said housing and having impedance compensating meanswithin said housing adjacent each of said ports, the cross-sectionaldimensions of the waveguide within said housing being substantiallyuniform in the plane normal to the bend, the sidewall of the bend on theoutside of the bend being defined by: a first surface substantiallycoplanar with one wall of the waveguide externally of said housingadjacent one of said ports, a second surface substantially coplanar withone wall of the waveguide externally of said housing adjacent the otherof said ports, and a third surface connecting said first and secondsurfaces, said third surface being generally arcuate away from thesidewall on the inside of the bend so that the cross-sectional dimensionof the waveguide within said housing in the plane of the bend along aline bisecting the angle of the waveguide bend is greater than thecorresponding dimension of the waveguide.
 2. The waveguide bend of claim1 wherein the angle of the waveguide bend is 90* and wherein the planeof the waveguide bend is the H plane.
 3. The waveguide bend of claim 1wherein the sidewall of the bend in the inside of the bend is definedby: a first surface substantially coplanar with one wall of thewaveguide externally of said housing adjacent one of said ports, asecond surface substantially coplanar with one wall of the waveguideexternally of said housing adjacent the other of said ports, and a thirdsurface connecting said first and second surfaces, said third surfacebeing substantially normal to said line bisecting the angle of the bend.4. The waveguide bend of claim 1 wherein said impedance compensatingmeans are located adjacent the sidewall on the inside wall of the bend.5. The waveguide bend of claim 1 wherein the dimension of the bend onsaid line bisecting the angle of the bend is between about 104 and 105percent of the dimension of the waveguide in the plane of the bend. 6.The waveguide bend of claim 5 wherein the angle of the waveguide bend is90* and wherein the plane of the waveguide bend is The H plane; and,wherein the sidewall of the bend in the inside of the bend is definedby: a first surface substantially coplanar with one wall of thewaveguide externally of said housing adjacent one of said ports, asecond surface substantially coplanar with one wall of the waveguideexternally of said housing adjacent the other of said ports, and a thirdsurface connecting said first and second surfaces, said third surfacebeing substantially normal to said line bisecting the angle of the bend.7. A broadband, low VSWR, double mitered waveguide bend for a hollowpipe waveguide having rectangular cross-sectional dimensions comprisinga waveguide bend defining housing having two ports adapted to be alignedwith the waveguide for the efficient transmission of electromagneticenergy through said housing and having impedance compensating meanswithin said housing adjacent said ports, the cross-sectional dimensionsof the waveguide within said housing being substantially uniform in theplane normal to the bend, the sidewall of the bend on the outside of thebend comprising two discrete surfaces intersecting in a plane bisectingthe angle of the bend, said intersecting surfaces forming an obtuseangle facing the sidewall on the inside of the bend so that thecross-sectional dimension of the waveguide within said housing in theplane of the bend along a line bisecting the angle of the waveguide bendis greater than the corresponding dimension of the waveguide.
 8. Thewaveguide bend of claim 7 wherein the dimension of the bend on said linebisecting the angle of the bend is between about 104 and 105 percent ofthe dimension of the waveguide in the plane of the bend.
 9. Thewaveguide bend of claim 8 wherein the sidewall of the bend on the insideof the bend is defined by: a first surface substantially coplanar withone wall of the waveguide externally of said housing adjacent one ofsaid ports, a second surface substantially coplanar with one wall of thewaveguide externally of said housing adjacent the other of said ports,and a third surface connecting said first and second surfaces, saidthird surface being substantially normal to said line bisecting theangle of the bend; and wherein said impedance compensating meanscomprises an element of electrically conducting material adjacent thesidewall on the inside of the bend.
 10. The waveguide bend of claim 9wherein the angle of the bend is 90* and wherein the plane of the bendis the H plane.
 11. The waveguide bend of claim 7 wherein the angle ofthe bend is 90* and wherein the plane of the bend is the H plane.
 12. Abroadband, low VSWR, double mitered waveguide bend for a hollow pipewaveguide having rectangular cross-sectional dimensions comprising awaveguide bend defining housing having two ports adapted to be alignedwith the waveguide for the efficient transmission of electromagneticenergy through said housing and having impedance compensating meanswithin said housing adjacent said ports, the cross-sectional dimensionsof the waveguide within said housing being substantially uniform in theplane normal to the bend, the sidewall of the bend on the inside of thebend comprising two discrete surfaces forming at their intersection on aline bisecting the angle of the bend an obtuse angle facing the sidewallof the bend on the inside of the bend so that the cross-sectionaldimension of the waveguide within said housing in the plane of the bendalong said line bisecting the angle of the bend is greater than thecorresponding dimension of the waveguide.
 13. The waveguide bend ofclaim 12 wherein the sidewall of the bend on the outside of the bend isdefined by: a first surface substantially coplanar with one wall of thewaveguide externally of said housing adjacent one of said ports, asecond surface substantially coplanar with one wall of the waveguideexternally of said housing adjacent the other of said ports, and, Athird surface connecting said first and second surfaces, said thirdsurface being substantially normal to said line bisecting the angle ofthe bend.
 14. The waveguide bend of claim 12 wherein the angle of thewaveguide bend is 90*, and wherein the plane of the waveguide bend isthe H plane.
 15. The waveguide bend of claim 12 wherein the waveguidebend as defined by said sidewalls includes an even number of waveguidesections, a first pair of said sections being of equal length and widerin cross-section in the plane of the bend at their intersection on saidline bisecting the angle of the bend than on their respectiveintersection with one of a second pair of said waveguide sections, saidsecond pair of said sections being of equal length and being wider incross-section in the plane of the bend at said ports than at theirrespective intersection with said first pair of sections.
 16. Thewaveguide bend of claim 15 wherein the number of waveguide sections inthe bend is four and wherein the dimension of the bend in the planethereof on a line bisecting the angle of the bend is between about 104and 105 percent of the dimension of the waveguide in the plane of thebend.
 17. The waveguide bend of claim 16 wherein the angle of the bendis 90*, and wherein the bend is the H plane.
 18. The waveguide bend ofclaim 12 wherein the sidewall of the bend on said outside of said bendis defined by a planar surface normal to said line bisecting the angleof the bend and a pair of arcuate surfaces on opposite sides thereof,said arcuate surfaces being substantially tangential both to said planarsurface and to the sidewalls of the waveguide at said ports.
 19. Thewaveguide bend of claim 18 wherein the angle of the bend is 90*, whereinthe plane of the bend is the H plane, and wherein the radius ofcurvature of said arcuate surface is between about 118 and 120 percentof the dimension of the waveguide in the plane of the bend.
 20. Abroadband, low VSWR, double mitered waveguide bend for a hollow pipewaveguide having rectangular cross-sectional dimensions comprising awaveguide bend defining housing having two ports adapted to be alignedwith the waveguide for the efficient transmission of electromagneticenergy through said housing, the cross-sectional dimensions of thewaveguide within said housing being substantially uniform in the planenormal to the bend, said waveguide bend including an even number ofwaveguide sections, a first pair of said sections being of equal lengthand wider in cross-section in the plane of the bend at theirintersection on a line bisecting the angle of the bend than on theirrespective intersection with one of a second pair of said waveguidesections, said second pair of said sections being of equal length andbeing wider in cross-section in the plane of the bend at said ports thanat their respective intersection with said first pair of sections, saidintersections being spaced such that discontinuities defined therebyinteract to reduce the VSWR of the bend over a broadband of frequencies.21. The waveguide bend of claim 20 wherein the number of waveguidesections in the bend is four and wherein the dimension of the bend inthe plane thereof at the intersection of said first and second pair ofsections is between about 91 and 95 percent of the dimension of thewaveguide in the plane of the bend.
 22. The waveguide bend of claim 20wherein the dimension of the waveguide bend in the plane of the bend atthe intersection of said first pair of sections is between about 104 and105 percent of the dimension of the waveguide in the plane of the bend.23. The waveguide bend of claim 22 wherein the dimension of thewaveguide bend in the plane thereof at the intersection of said firstand second sections is between about 91 and 95 percent of the dimensionof the waveguide in the plane of the bend.
 24. The waveguide bend ofclaim 23 wherein the Plane of the bend is the H plane; and wherein theangle of the bend is 90*.
 25. The waveguide bend of claim 20 wherein theangle of the waveguide bend is 90* and wherein the plane of the bend isthe H plane.
 26. The waveguide bend of claim 25 wherein the number ofwaveguide sections is four, and wherein the dimension of the bend in theplane of the bend along said line bisecting the angle of the bend isbetween about 104 and 105 percent of the dimension of the waveguide inthe plane of the bend.
 27. A broadband, low VSWR, double miteredwaveguide bend for a hollow pipe waveguide having rectangularcross-sectional dimensions comprising a waveguide bend defining housinghaving two ports adapted to be aligned with the waveguide for theefficient transmission of electromagnetic energy through said housing,the cross-sectional dimensions of the waveguide within said housingbeing substantially uniform in the plane normal to the bend, theeffective cross-sectional dimension of the waveguide within said housingin the plane of the bend along a line bisecting the angle of thewaveguide bend being greater than the corresponding dimension of thewaveguide, and, the effective cross-sectional dimension of the waveguidewithin said housing in the plane of the bend adjacent said ports beingless than the corresponding dimension of the waveguide, said differingeffective cross-sectional dimensions interacting to reduce the VSWR ofthe bend over a broadband of frequencies.